The present invention relates to novel bisacylphosphine oxides, the preparation thereof, and their use as photoinitiators in photopolymerizable compositions.
A number of photoinitiators based on acylphosphines are known. U.S. Pat. No. 3,668,093 and German Offenlegungsschrift No. 3,020,092, for example, describe acylphosphines as photoinitiators. European publication Nos. 0 73 413, 0 007 508, 0 057 474 describe monoacylphosphine oxides as photoinitiators. However, photopolymerizable compositions cured with the initiator systems of U.S. Pat. No. 3,668,093 exhibit unsatisfactory color stability and photopolymerizable compositions cured with the initiator systems of U.S. Pat. No. 3,668,093, German Offenlegungsschrift No. 3,020,292, and the European publication Nos. 0 073 413, 0 007 508 and 0 057 474 cure only to a shallow depth, have low curing rates and exhibit unsatisfactory storage stability. Furthermore, it is a disadvantage that the initiators of the above publications only have a low absorption in the range of visible light, i.e., wavelength &gt;400 nm, so that only low light yields can be attained in this range. However, the use of this "harmless" light is particularly indispensable for many applications, e.g. in the dental field.